1. Field of the Invention.
This invention has relation to the illumination of levels in which an elongate main frame is provided with a flat plane working surface and a plurality of sight ports. A plurality of bubble vials are fixedly mounted in the frame across the sight ports to have permanently fixed angular relationship with respect to the working surface. The invention also has relation to providing means to illuminate the position of the bubbles within the vials in the form of a kit to retrofit existing levels.
2. Description of the Prior Art.
It has long been recognized as advantageous to provide illumination of bubble vials of levels. For instance, as an electrician, the present inventor must level, plumb and install many electrical conduits and other elements in new buildings before permanent lighting is available in such buildings. The need for illuminated bubble vials in levels has been recognized in the following U.S. Pats. Nos.: 1,566,541 for ELECTRIC LIGHT ATTACHMENT FOR LEVELS granted to Kirby in December of 1925; 2,198,945 for ILLUMINATED LEVEL granted to Morriss in April of 1940; 2,543,572 for ILLUMINATED SPIRIT LEVEL HAVING A RECESSED BATTERY-RECEIVING WEB granted to Friberg in February of 1951; 2,607,882 for ILLUMINATED LEVEL granted to Arnold in August of 1952; 2,615,122 for ILLUMINATED LEVEL granted to Coombs in October of 1952; 2,652,481 for ILLUMINATED LEVEL granted to Hall in September of 1953; and 2,806,133 for ILLUMINATED SPIRIT LEVEL granted to Aube in September of 1957.
While none of the structures shown in these patents has been known to find wide acceptance in the marketplace, and while none are readily available on the market today, they all suffer from difficulties which render them more or less unsuitable for their intended purpose. For example, most appear to be several feet long, and while this length may actually be an advantage for many uses, it is unsatisfactory for use by construction workers such as plumbers and electricians who must align building components in confined quarters.
All of the patents cited above rely on electric light bulbs, the filaments of which break the first or second time they are dropped to the floor. Such levels are not rugged enough for general day-in and day-out usage by construction workers or others.
All of the patents cited above show structures which rely on light sources which illuminate the general area of sight ports containing lighted vials. Such patents do not disclose means to provide a light source which directs the light into end portions of each bubble vial to cause the light to travel through the liquid within the vial to impinge on the surface of the bubble to make it a reflective surface, and as such, to more sharply define the position of the bubble in the vial.
One such patent, the patent to Arnold, discloses a retrofit arrangement whereby "an elongated substantially rectangular support plate 34" (also called "a combined reflector and support plate") holds flashlight members and completely blocks off each of the sight ports from one side. This shields the vials from ambient light and even in the day time would require artificial illumination either from the level itself or from light coming from behind the user.
What was needed before the present invention was a rugged, droppable level in which light sources are situated at the opposite ends of bubble vials to illuminate the liquid within the vials so that the boundary walls between the bubbles and the liquid are sharply defined; the overall level being of dimension to fit easily within the pocket or tool pouch on the body of the user between uses.
Also needed was a retrofit structure which could be applied to an existing level to meet the needs set out above. An excellent level to modify with such a retrofit structure to meet at least all of these needs is a level about nine inches long, sold by Sears under the trademark CRAFTSMAN, Model No. 939829. Such a level is sold marked PAT. NO. 4,463,501. That patent was granted to Wright et al. in August of 1984.
Neither the inventor nor those in privity with him are aware of any prior art which is closer than that discussed above, and are aware of no prior art which anticipates the claims made herein.